How is missing information on risk-factors dealt with?

Patients with missing date of surgery are excluded, and multiple imputation, with 10 imputed datasets, is used to fill in any missing information on the risk factors. The method, known as Multiple Imputation using Chained Equations, uses a patient’s other risk-factors to predict their missing information, whilst taking into account the uncertainty due to their missing information. In addition to the data items in the risk-adjustment model, and the outcomes, the following items are used to predict missing risk-factors: surgical urgency, mode of admission according to NBOCA, surgical procedure, number of lymph nodes extracted, number of positive lymph nodes extracted, Index of Multiple Deprivation, length of hospital stay, and days from diagnosis to surgery.